1. Field of the Invention
The present invention relates generally to stents, stent loading, stent contracting and stent delivery systems and their respective methods of use. Some embodiments of the invention are more specifically directed to stent loading and crimping systems which are configured for reduced frictional interface between a stent and one or more system component which contact the stent during the crimping and loading process.
2. Description of Related Art
A stent is a generally tubular device that is used to support a bodily lumen. A stent is typically delivered to a desired bodily location via a catheter. Often the stent is loaded onto a portion of the catheter, such as a balloon or other region of the catheter shaft. In some stent delivery systems the stent is crimped to the catheter in order to minimize the profile of the stent on the catheter and to prevent undesired movement of the stent relative to the catheter shaft.
A number of techniques for loading and contracting a stent to a catheter shaft or balloon are used. One such technique that is commonly used in the radiological suite involves hand crimping the stent to the balloon. A stent is placed over an uninflated balloon and then squeezed with the fingers until the stent is in intimate contact with the uninflated balloon. The technique is highly operator dependent and can affect stent profile and stent placement with respect to the balloon and radiopaque markers. It can also affect the dilatation length of the stent and lead to pinching of the balloon.
Other techniques for crimping stents involve the use of mechanical devices for crimping stents. Mechanical stent crimpers have been disclosed in a number of patents including U.S. Pat. Nos. 6,387,118; U.S. Pat. No. 6,360,577; U.S. Pat. No. 6,108,886; U.S. Pat. No. 6,092,273 U.S. Pat. No. 6,082,990; U.S. Pat. No. 6,074,381; U.S. Pat. No. 6,063,102 and U.S. Pat. No. 5,992,000. Mechanical stent have also been disclosed in a number of copending, commonly assigned patent applications including U.S. application Ser. Nos. 09/401467, 09/401213, and 09/404986.
In many current stent loading operations particularly those involving self-expanding nitinol or shape memory stents the stent is dipped or sprayed with liquid nitrogen or other cooling agent in order for the stent to achieve a martensitic state. While in the martensitic state the stent is constrained via a crimper or other reducing device. In some cases the crimper comprises an adjustable stent diameter reducing chamber or opening through which the stent is advanced in order to uniformly reduce or compress the stent about its circumference.
Stent crimpers may have a variety of configurations and mechanisms for providing the stent diameter reduction chamber. For example, an iris type chamber wherein a plurality of members or blades are moved relative to the stent to reduce or expand the diameter of the chamber is described in U.S. Pat. No. 6,360,577, a crimper having a chamber defined by a plurality of member which extend inward to contract the chamber in a “star” or other geometric configuration is described in U.S. Pat. No. 6,168,921, a crimper having a pair of jaws or members that are moved relative to one another to reduce or expand the diameter of the chamber is described in U.S. Pat. No. 6,387,117, and a crimper having one or more conical apertures which at least partially define the chamber is described in U.S. Pat. No. 5,992,000. Crimpers having other configurations are also known. The entire content of each of the references cited above are incorporated herein by reference.
In many crimper assemblies a mandrel or push rod is utilized to drive the stent through the closed iris into a stent delivery mechanism such as a catheter.
In many crimper designs however, the crimping members or blades will come into direct contact with the stent being crimped as the iris is closed radially inward about the stent. After the stent has been reduced in diameter, in many instances the blades are kept in direct contact with the stent in order to keep the stent in the reduced state prior to loading of the stent onto a catheter or other delivery system. The stent is then transferred from the iris onto the delivery system by advancing a push rod or mandrel through the closed iris. In order to expel the stent from the iris the longitudinal force exerted on the stent by the mandrel must be sufficient to disengage the stent from its contact with the blades. If the force exerted on the stent by the mandrel is greater than the column strength of the stent the stent will buckle thereby leading to an unsuccessful loading of the stent. Unfortunately, such excessive force is often required to remove the stent from the crimper.
In addition to potentially buckling the stent, the force exerted by direct contact of the crimper blades on the stent as well as the act of pushing the stent out of the iris may have significant impact on any coating the stent may have even if the force is not excessive. For example where the stent includes one or more therapeutic coatings (i.e. a drug coated stent), direct contact of the stent by the blades during reduction, and/or the frictional interface of the blades and the stent during expulsion of the stent from the iris, may result in impairment of the coating thus reducing or negating its effectiveness.
In light of the above there is a need to provide stent reducing/loading systems with the capability to reduce and expel a stent, especially those stents having a therapeutic coating, from the reducing mechanism with reduced force and preferably with reduced contact between the stent and the reducing mechanism and/or push rod or support mandrel.
All US patents, applications and all other published documents mentioned anywhere in this application are incorporated herein by reference in their entirety.
Without limiting the scope of the invention a brief summary of some of the claimed embodiments of the invention is set forth below. Additional details of the summarized embodiments of the invention and/or additional embodiments of the invention may be found in the Detailed Description of the Invention below.
A brief abstract of the technical disclosure in the specification is provided as well only for the purposes of complying with 37 C.F.R. 1.72. The abstract is not intended to be used for interpreting the scope of the claims.